1. Field of the Invention
The present invention targets the field of offset printing suited for various kinds of small lot purposes.
2. Description of Related Art
Offset printing is a typical printing method where a plate in which hydrophilic portions and hydrophobic (lipophilic) portions corresponding to image information are formed is used to form an image on a recording medium by applying dampening water to the hydrophilic portions and selectively applying ink only to the hydrophobic portions and transferring the ink to the recording medium.
Offset printing method is a typical image forming method using a planographic printing plate. In the offset printing method, a planographic printing plate in which hydrophilic portions and hydrophobic (lipophilic) portions are formed on the surface corresponding to image information is made, and thereafter, an image is formed on a recording medium by applying dampening water W to the hydrophilic portions of the planographic printing plate, forming an ink image on the planographic printing plate by applying ink to the lipophilic portions and transferring the ink image on a recording medium. Such offset printing enables to continuously carry out image forming on a great number of recording media.
However, the planographic printing plate used for offset printing includes a hydrophobic photosensitive layer which is provided on a hydrophilic support formed of aluminum or the like and exposure process and etching process corresponding to image information are carried out to remove the photosensitive layer in non-image area. Therefore, complicated plate making process or waste disposal process needs to be carried out.
In view of the above, there is suggested a manufacturing method of a planographic printing plate (hereinafter, called a plate) in which the making process is easy (for example, see JP H10-16420 and JP H11-227351).
The technique described in JP H10-16420 is a technique to make a plate by recording the heat-melt transfer recording medium (ink ribbon) on a hydrophilic support including zinc oxide by a melt-transfer printer.
The technique described in JP H11-227351 is a technique to make a plate by forming a plate image on an original plate by an electrographic copier or printer by using sphere toner.
In both of the above techniques, the durable number of times of printing is decreased comparing to the offset printing. However, the process of making the plates is easy and wastes can be minimized.
However, by the techniques described in JP H10-16420 and JP H11-227351, the plate on which a plate image is once formed cannot be reused by forming a new image onto the plate, and a plate image needs to be formed by using a new plate even when one sheet or only a few images are to be printed. Therefore, these techniques are not suited for a so-called variable printing. Further, there is a problem that waste is increased because same plate cannot be used.